Nutritional supplements, especially vitamin and mineral supplements, are widely utilized by people throughout. They are substantial contributors to overall intakes since the number of micronutrients they give varies widely, from well below recommended intakes to far above them. Despite the fact that supplements can be used to treat or prevent micronutrient deficiencies, the vast majority of people who take them do so without experiencing any symptoms of nutritional insufficiency. Yet, vitamin and mineral supplements and their impact on the risk of non-communicable diseases in “generally healthy” populations are contentious. We look at how supplements are used and how randomized controlled trials have shown their efficacy.

Who uses supplements?

Although the market for vitamin and mineral supplements is enormous, this discussion will focus on the Western Hemisphere because this is where the majority of research has been conducted. North American folks regularly use dietary supplements such as vitamins, minerals, and fish oil. Some nutrients, like vitamin D, have seen a rise in popularity as people seek to boost their intake while others, like multivitamins and minerals, have seen a decline in popularity. Supplemental omega-3 fatty acid consumption also saw a sevenfold rise.

While supplement use is more common in the United States and Canada, it is much lower in other nations (e.g., 51% in Denmark, 34% in South Korea, 43% in Australia, 36% in the United Kingdom, 6% in Spain, and 2% in Greece). The difference in prevalence between low- and high-income nations may be attributable to the varied methods used to evaluate supplement consumption. Unfortunately, there is a lack of national survey data for supplement use in the general population in low and middle-income countries.

Subgroups of the North American and European populations have widely varying rates of supplement consumption. Seventy percent or more of seniors aged 65 and above in the United States consume supplements, whereas just one-third of kids and teenagers do. Supplements are used by more women than men. There is a significant positive relationship between supplement consumption and both level of education and income. It also tends to go together with other indicators of a healthy lifestyle, such as avoiding smoking or drinking excessively, maintaining a healthy weight, and engaging in regular physical activity. Most people who take vitamins and minerals have a healthier diet overall than those who don’t, and their dietary consumption of essential nutrients is generally higher than the recommended amounts.

In poor and middle-income countries with frequent micronutrient deficiencies, supplementation is indicated if food-based strategies like dietary change, fortification, or food provision fail (for example, iodine, iron, zinc, and vitamin A). Dietary fortification and enrichment have practically eliminated deficiency disorders in the US and abroad. Iodine, vitamin D, and B1 and B3 vitamins have been added to salt, milk, and refined bread (goiter, rickets, beriberi, and pellagra, respectively).

In high-income countries, where vitamin and mineral supplement use is higher, intake above the acceptable upper limit appears to be rising. While less than 5% of U.S. adults exceed the upper threshold, certain population subgroups may overconsume. In one national Canadian study, almost 80% of 1-3-year-olds received too much vitamin A and niacin. Supplemented toddlers in the US have 97% vitamin A and 68% zinc. It is difficult to determine if overconsumption of several nutrients is harmful due to a lack of high-quality research.

Do supplements protect against non-communicable diseases?

1. Cancer

Some data suggest vitamin and mineral supplementation may hinder cancer prevention. Two randomized trials found that β-carotene supplementation increased lung cancer risk in high-risk patients. The α-Tocopherol, β-Carotene Cancer Prevention Study found an 18% relative risk increase in smokers randomly assigned 20 mg/day β-carotene. The β-Carotene and Retinol Effectiveness Study found that β-carotene (30 mg/day) and vitamin A as retinol (25 000 IU/day) elevated risk by 28% among smokers and employees with occupational exposure to asbestos. Vitamin E (400 IU/day) supplementation increased prostate cancer risk by 17% in the Selenium and Vitamin E Cancer Prevention Experiment.

In nations with obligatory fortification, increased folic acid exposure may promote cancer progression, even though maternal supplementation reduces neural tube defect risk. Specifically, folic acid supplementation at 1 mg/day may cause undetected colorectal adenomas. A meta-analysis of 11 randomized studies found that folic acid supplementation did not raise or decrease site-specific cancer risk within five years.

Although some evidence of reduced total cancer mortality, vitamin D supplementation alone or with calcium has not been shown to reduce cancer risk at either high or moderate dosages in randomized studies. Fish oil supplementation does not reduce cancer risk, according to limited research. 

2. Type 2 diabetes

Supplementing with vitamins C and E, beta-carotene, or fish oil has not been shown to reduce the risk of type 2 diabetes, and the overall evidence from randomized studies is weak. Vitamin D supplementation (4000 IU/day) failed to reduce the risk of type 2 diabetes in a recent placebo-controlled experiment, while considerably raising serum 25-hydroxyvitamin D concentrations.

3. Cardiovascular disease

After the 2013 USPSTF review20, a comprehensive review of 15 randomized trials found no effect of supplements on cardiovascular events, mostly in risk factors. Folic acid alone or with vitamins B12 or B6 lowered plasma homocysteine, but total cardiovascular events did not. Another comprehensive analysis found that homocysteine-lowering B vitamins lowered stroke risk, although it was mostly driven by one big Chinese trial.  Antioxidant supplements are not proven to lower cardiovascular risk. 

One of the few randomized trials of supplements for primary cardiovascular disease prevention, the Vitamin D and Omega-3  (VITAL), found no benefit of vitamin D supplementation (2000 IU/day) on its primary endpoint (myocardial infarction, stroke, or cardiovascular death) in healthy people.

The Women’s Health Initiative Calcium and Vitamin D Supplementation and the Vitamin D Assessment both found no cardiovascular risk benefit from vitamin D supplements. Omega-3 fatty acids (1 g/day) did not reduce major cardiovascular events in healthy persons in the VITAL study.

Nonetheless, overall myocardial infarctions were improved. This supports meta-analyses that found fish oil supplementation did not protect against cardiovascular disease.  A meta-analysis of recent trials showed a considerable reduction in myocardial infarction risk.  Fish oil supplementation may reduce heart disease risk more than stroke risk. Further research is needed.